Phase 11: remote UX & network attach (0.11.0)

- Live remote-stack logs over a WebSocket proxied through the central app to
  the agent (/ws/agent-logs/{agent}/{stack}); agent gains a WS log endpoint.
- Deploy to a remote host from the UI: host selector in the New Stack editor
  and template dialog; templates instantiate onto an agent via the proxy.
- Network attach/detach: expandable inspect view per network with
  connect/disconnect + container picker; GET /{id}/containers, POST connect/disconnect.
- Remove dead pages/Placeholder.tsx.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/routers/ws.py

@@ -4,10 +4,16 @@ from __future__ import annotations
 import asyncio
 import json
 
+import contextlib
+
+import websockets
 from fastapi import APIRouter, Query, WebSocket, WebSocketDisconnect
 from jose import JWTError
+from sqlmodel import Session
 
 from auth import decode_token
+from database import engine
+from models.agent import Agent
 from services import compose_service
 
 router = APIRouter(tags=["ws"])
@@ -82,6 +88,47 @@ async def ws_service_logs(
         pass
 
 
+@router.websocket("/ws/agent-logs/{agent_id}/{stack_id}")
+async def ws_agent_logs(
+    websocket: WebSocket,
+    agent_id: int,
+    stack_id: str,
+    token: str | None = Query(default=None),
+):
+    """Proxy live compose logs from a remote agent through to the browser."""
+    await websocket.accept()
+    if not await _authorize(websocket, token):
+        return
+
+    with Session(engine) as session:
+        agent = session.get(Agent, agent_id)
+    if not agent:
+        await websocket.send_text(json.dumps({"type": "error", "detail": "agent not found"}))
+        await websocket.close()
+        return
+
+    base = agent.url.rstrip("/")
+    ws_url = ("wss://" + base[8:] if base.startswith("https://")
+              else "ws://" + base[7:] if base.startswith("http://")
+              else "ws://" + base)
+    ws_url += f"/agent/ws/logs/{stack_id}?token={agent.token}"
+
+    try:
+        async with websockets.connect(ws_url, open_timeout=10, ping_interval=20) as upstream:
+            async for message in upstream:
+                await websocket.send_text(
+                    message if isinstance(message, str) else message.decode("utf-8", "replace")
+                )
+    except WebSocketDisconnect:
+        pass
+    except Exception as exc:  # noqa: BLE001
+        with contextlib.suppress(Exception):
+            await websocket.send_text(json.dumps({"type": "error", "detail": str(exc)}))
+    finally:
+        with contextlib.suppress(Exception):
+            await websocket.close()
+
+
 @router.websocket("/ws/events")
 async def ws_events(
     websocket: WebSocket,